i found another limit switch (?) on the dryer's vent.i checked it by bypassing it as i did with the limit switches above the heater element - no difference evident.i tested it too...i found this cylindrical part too, situated by the motor;

The thermostats on the heater box are (left) a one-shot safety and (right) a 109c operating thermostat. They are replaced as a pair, p/no 1701896. If the safety has failed, the disc on the front will be dished inwards.

The single commonest cause of failure is opening the door whilst the dryer is running at full heat.

Element failure is usually caused by foreign object damage, typically bra wires being forced through the back of the drum.